This invention relates to a scissor action tool and more particularly to garden shears or the like which are especially suitable for cutting grass but can also cut thin branches and hedges, and are provided with a pair of cooperatively engaging cutting elements united for scissor action about a joint.
The nearest prior art for the present invention is represented by long-arm tools with scissor-type function, used primarily for cutting grass and straws at the level of the ground surface, the user being in a standing position. It is to be noted, for the sake of clarity, that such grass cutters are used, above all, in finishing cuttings around trees, stones or the like objects.
In practice, these kinds of tools comprise a pair of blades which are pivoted to move relative to each other in a scissor-like manner relative to one pivotal point. The hand levers of the scissors have long arms to such an extent that the user can cut grass without having to bend down. Further, handle bars are typically positioned at the end of the arms in a horizontal position. To enable cutting with the tool in the first place, the pivotal point between the blades must be in a horizontal direction sufficiently far from the hand levers. This distance is the lever arm by means of which the blades can be subjected to shear force. In practice, the arms will thus be located for example at an angle of 45 degrees relative to the horizontal plane, the actual blades and correspondingly the handle bars being in a substantially horizontal plane.
This geometry causes two problems. Firstly, the bolt forming the pivotal point in practice is subjected to adverse and, as regards the cutting, unnecessary torque, which is brought about by the force moving the handle bars towards each other multiplied by the vertical distance between the pivotal point and the hand levers. In order for the structure to be able to bear this torque, it must be made unduly heavy. Secondly, the structure brings about torque in the handle bars, due to the center of mass of the cutters being clearly on the front side of the handle bars, in practice often relatively close to the pivotal point of the blades. Resisting this torque causes static tension in the user""s wrists, which easily makes it heavy and unpleasant to use a tool of this kind.
It is an object of the present invention to provide a scissor action tool as described above, particularly long-arm multi-purpose garden scissors which do not have the above problems relating to the conventional design. This object is achieved by providing a scissor action tool, comprising first and second cutting elements pivotable about a first joint in a first plane of movement, first and second hand levers pivotable about a second joint in a second plane of movement, one end of said first cutting element being pivotally connected to one end of said first hand lever at a third joint and one end of said second cutting element being pivotally connected to one end of said second hand lever at a fourth joint, a line connecting said third and fourth joint forming a meeting line between said first and second plane of movement and said third and fourth joint allowing the angle between said first and second plane of movement to be adjusted.
The structure utilized in the tool according to the invention allows adjustment of the angle between the arms and the blades, whereby, for example, an angle of 90 degrees may be used when grass is cut, in which case torque straining the user""s hands is not generated at all, because the center of mass is directly downwards from the user""s hands. The above-mentioned property of the tool according to the invention is facilitated by the fact that said first and second hand levers comprise at one end handle bars extending at an approximately right angle from the hand levers.
A preferred way to implement a pivotal point in which the blades and arms are joined to each other is to implement the structure in such a way that said third and fourth joint each comprises a cylindrical seat attached to said one end of one of said hand levers and having an axis parallel to said second plane of movement, a first insert received by said seat, having a cylindrical contour co-operating with the inner surface of said seat and an end surface facing outwards from said seat, and provided with a cylindrical boring going through said first insert transverse to the axis of said cylindrical contour of said first insert and opening to said end surface of said first insert, a second insert received by said cylindrical boring of said first insert, having a cylindrical contour co-operating with the inner surface of said boring, and provided with a longitudinal slot for receiving said one end of one of said cutting elements, said end being provided with a hole, and with a transverse hole for receiving a pin extending through said hole in said cutting element to lock said cutting element pivotably in said slot.